Make a bad café con leche in Humboldt Park and you’ll hear about it from the Bench Mob, a cluster of older Puerto Rican men who’ve gathered to play dominoes in the park for decades. The Bench Mob polices the park from sunup to sundown, eating from the half-dozen frittura trucks (trailers hawking fried snacks) and hollering out in Spanish to teenagers to lower the beats booming out of their cars. But while this older generation is protective of tradition, from music etiquette to the foods eaten and sold, a new generation hopes to break the homogeneity.

“We live a block away and walk the park all of the time… one day we were craving good coffee,” Cristina Ayala says, her husband, Juan, nodding in agreement. “We decided to do it ourselves. I researched food trucks, put together a business plan and talked to the Chicago Park District, who were completely supportive. But then we had to get through the Cocineros Unidos, which is like the Humboldt Park Puerto Rican union.”

Much like the Bench Mob, Cocineros Unidos—a coalition of local business owners—has existed for around 30 years. The Ayalas played the game, attending the group’s meetings, reaching out to their alderman and pointing out that they’re both of the local Latino community. After a year of persuasion, the couple convinced the powers that be that the park could use some new blood, specifically in the form of a gleaming 1967 Airstream putting out coffee drinks, tropical fruit batidas (smoothies), toasted sandwiches and Puerto Rican pastries.

The Park District permit means Isla De Café plays by different rules than food trucks on city streets, so Juan (an engineer by trade) retrofitted the trailer to hold equipment that allows the staff to cook and concoct to order. A panini press melts Muenster into ham between eggy, sugar-dusted bread for the malloraca, a Latin-American monte cristo. The Peruvian-inspired tuna brava employs ceviche ingredients—ají Amarillo, lime, salt—piling the spicy fish onto sobao-style bread from Guadalajara Bakery. A pastrami sandwich is done as it is on modern food trucks in Puerto Rico: piled high with grilled onions, white cheese and mustard then toasted to order.

As good and as cheap as the sandwiches are (topping out at $4.25), café is the trailer’s backbone. Pulled-to-order shots of Metropolis espresso are offered naked as pocillo, with caramelly sugar as a Cubano, with milk for a cortado and spiked with anise syrup for the chichaito. So far, the Bench Mob has been reluctantly approving. “I played Buena Vista Social Club and they protested right away,” Cristina says. “[They said,] ‘Hey, you’re playing Cuban music, that’s not Puerto Rican, play Puerto Rican music!’ But even then, they still say, ‘El café! El café es delicioso.’ ”